Array protection devices and fabrication method

ABSTRACT

The present disclosure sets forth an improved integrated circuit in which circuit elements, adjacent to a fuse, are protected by barriers positioned adjacent the fuse. In the improved integrated circuit the barriers are non-frangible, high melting point structures buried in the passivating layer, covering a wiring layer containing a fuse, and are between the fuse and adjacent circuit elements in the wiring layer structures. 
     Also taught is a method of protecting circuit elements adjacent a fuse comprising the steps of depositing an insulating layer on the surface of a semiconductor device having active regions therein, forming a plurality of fuses and circuit elements in said layer, coating said fuses and elements with a second insulating layer, patterning said second insulating layer to form grooves between each of said fuses and any adjacent fuse or circuit element, and depositing a high melting point and non-frangible material in said grooves.

This is a divisional of application Ser. No. 08/221,715 filed on Mar.31, 1994 now U.S. Pat. No. 5,420,455.

FIELD OF THE INVENTION

This invention relates to semiconductor integrated circuits which can betailored by cutting lines in the circuit and, more particularly, to suchcircuits which have built therein barriers devices adjacent each line tobe cut. These barriers prevent accidental injury to nearby circuitelements when the circuit is tailored. The invention further relates tothe method of making the improved circuit.

BACKGROUND OF THE INVENTION

Semiconductor integrated circuits are formed in a body of semiconductormaterial having active regions therein which are joined in a desiredcircuit configuration by a plurality of wiring layers laid down on thesurface of the body.

Many semiconductor integrated circuits, such as logic circuits, aredesigned to be tailored, after manufacture, to provide certain logicalcombinations or meet other selected criteria. To permit such tailoringsuch circuits are designed with circuit alteration devices, typicallyand hereinafter referred to as fuses, which are usually in the form oflines that can be physically broken or cut to thereby alter the circuitfrom its original configuration. This tailoring ability is provided insuch circuits, during the circuit design and is included as part of thewiring layers of the circuit.

In the manufacture of the circuit, these wiring layers are deposited anddefined and interconnected with conductive vias through a series of wellknown photolithography and metal etching steps. Each such wiring levelis coated with a layer of a glassy protective material, known as apassivation layer, which protects and insulates the wiring of eachlayer. The creation of integrated circuits with such multiple wiringlayers is well known to the semiconductor art.

In such circuits it has been found that if the lines or fuses are formedwith positive side slopes, they offer distinct advantages over line withnegatively sloped side wall. The advantages are especially realizedduring the fabrication of the wiring levels, the subsequent depositionof the passivation layer, and the formation of the interconnection vias.

In some circuits, such as CMOS logic circuits, the fuses, designed inthe circuit are usually formed in regular arrays in the upper mostlayers of wiring and in a position such that other wiring is not placedimmediately thereover. In such arrays the fuses are often aligned inparallel rows and placed as closely together as is possible. By openingselected ones of these fuses the logic elements of the circuits can bearranged in different combinations to perform different logic functions.

These fuses are typically opened by applying a laser pulse of sufficientsize, duration and power as to superheat and vaporize the metal formingthe fuse. This superheating of the fuse and its vaporization fracturesand blows away a portion of the overlying glassy protective layercreating a saucer shaped crater in the protective layer. When theprotective layer ruptures, cracks can radiate outwardly causingadditional damage such as breakage of or the uncovering of adjacentelements. Such uncovering of the adjacent elements can cause subsequentcorrosion and premature failure of the circuit. Furthermore, there is noknown means of repairing any of the adjacent circuit elementsaccidentally altered by the blowing of an adjacent fuse.

It has been found that when the fuse, being blown, has sides with apositive slope these effects are worsened because the beam, used tovaporize the fuse, is reflected therefrom and can cause partial meltingand reflowing of adjacent circuit elements altering their resistive andcapacitive characteristics and hence the circuit to which they areconnected.

To prevent such damage to the adjacent elements, the prior art couldprovide no solution except that of increasing the inter-element distancebetween the fuse, and the adjacent elements. This solution isundesirable. The entire direction in the integrated circuit art has beendirected towards reducing the size of the circuit and hence reducinginter-element dimensions to the smallest level possible. Thus, the onlyavailable solution was unacceptable but, until the present invention,there has been no other.

Accordingly, there now exists a need for an improved circuit arrangementwhich avoids all the above described problems associated with theblowing of such fuses as found in the prior art. The present invention,achieves these desirable results, by preventing both the beam energy andthe effects of the fuse blowing to reach or affect any adjacent elementin the circuit while maintaining the presently achievable, minimum,inter-element dimensions and all the other known advantages of such fusearrays.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved integratedcircuit in which circuit elements adjacent to the fuse are unaffectedwhen the fuse blows open.

It is another object of the present invention to prevent either theenergy, of the fuse blowing operation, or the effects of the fuseblowing to reach or affect any adjacent element in the circuit whilestill providing minimum inter-element dimensions and all the other knownadvantages of such fused circuits.

It is another object of the invention to provide all the above and otherobjects and advantages, of the present invention, in an integratedcircuit while using conventional integrated circuit materials andtechniques.

These desirable results and other objects and advantages, of the presentinvention, are realized and provided by, depositing between each circuitelement to be protected and the fuse being blown a body formed of a highmelting point, non-frangible material. In the present invention, thereis thus provided a semiconductor integrated circuit, having a pluralityof metallic structures on a surface thereof with one of the structuresbeing a fuse and a body of non-frangible, high melting point materialpositioned between the fuse and adjacent circuit elements.

These and other features are provided by the present invention whichrelates to a method of protecting adjacent circuit elements comprisingthe steps of depositing an insulating layer on the surface of asemiconductor device having active regions therein, forming a pluralityof fuses and conductors on said layer, coating said fuses and conductorswith a second insulating layer, patterning said layer with groovesbetween said fuses and any adjacent fuse or conductor and depositing ahigh melting point and non-frangible material in said grooves.

These and other objects, features, and advantages of the invention willbe apparent from the following more particular description of thepreferred embodiment of the invention as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a typical fuse array as used in an integratedlogic circuit.

FIG. 2 shows a section of the array of FIG. 1 taken along the lines2--2.

FIG. 3 shows the array of FIG. 1 after one of the fuses therein has beenblown by application of a laser beam.

FIG. 4 shows a section of the array of FIG. 3 taken along the lines4--4.

FIG. 5 shows a top view of a fuse array similar to that of FIG. 1 withthe present invention included therein.

FIG. 6 shows a section of the array of FIG. 5 taken along the lines6--6.

FIG. 7 shows the array of FIG. 5 after one of the fuses therein has beenblown by application of a laser beam.

FIG. 8 shows a section of the array of FIG. 7 taken along the lines8--8.

FIG. 9 shows a cross section of an integrated circuit having a fusearray and additional wiring levels.

FIG. 10 shows a cross section of a variation of the integrated circuitof FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Basically, the present invention, as will be more fully set forth below,describes an integrated circuit having a multiplicity of fuses andconductive lines on its surface.

Referring now to the drawings and especially FIGS. 1 to 4 there will begenerally described a method of producing an integrated circuit with afuse array therein. In these FIGS. 1-4 a semiconductor substrate 10 hascreated therein a plurality of active device regions (not shown)therein. The substrate 10 typically is formed of silicon but may be anysuitable semiconductor material. The active device regions are formed byprocesses well known to the semiconductor art.

Once all the active regions are formed in the substrate an insulatinglayer 12, about 10,000 Å in thickness, is formed over the surface 14 ofthe substrate 10. This layer 12 is typically formed by a chemical vapordeposit (CVD) of silicon oxide (SiO₂). A photoresist (not shown) is laiddown on top of the layer 12 and patterned to etch, by reactive ionetching, a plurality of via holes (not shown) in layer 12 to exposeselected portions of the active regions. The photoresist is then removedand metal via connectors (not shown) are deposited therein to provideconnectors from the active regions to the surface of layer 12. Oncethese connectors are formed a tri-level metal layer, typically about10,000 Å in thickness, is deposited over the layer 12 and defined into apredetermined metallization or wiring pattern illustrated by metal lines16, 18, and 20 by a suitable plasma etching process. Desirably, theselines are approximately 1.4 microns in width, at their widest point andare positioned 7.2 microns on center. Preferably this tri-level metallayer consists of outer layers 24 and 26 of titanium and acopper-aluminum core 28.

These lines can, in actuality, be fuses, resistors, capacitor plates, ormerely conductive lines interconnecting various portions of theintegrated circuit being built. In the present embodiment it will beassumed that these lines 16, 18, and 20 are designed as fuses in a logicarray. The fuses 16, 18, and 20 are usually created by coating thedeposited metal with a new photoresist layer, patterning the layer andthen exposing the metal layer to a suitable reactive ion etch. As shownin FIG. 2 this reactive ion etch causes the fuses 16, 18, and 20 to havepositive side slopes 16a, 18a, and 20a.

Once the lines 16, 18, and 20 are defined, the photoresist is removedand the entire substrate is coated with a passivation layer 22,typically formed of SiO₂, and ranging in thickness between 7500 Å and20,000 Å. The surface of this layer 22 is now planarized by knowntechniques. This layer 22 encloses and protects the defined wiringpattern. If additional levels of wiring are required the above describedprocesses can be followed to define the additional wiring levels as willbe later described in conjunction with FIGS. 9 and 10. All of the abovedescribed techniques are widely known and used in the semiconductor artand further description is not believed necessary.

Logic arrays are typically fabricated in a universal logic circuit andthen altered by selective cutting of lines, i.e., blowing the fuses,therein to form the final desired logic. Presently such selectivecutting of the lines is by a laser beam.

In the present example it will be assumed that to achieve the desiredconfiguration it is necessary that the central line 18 or fuse is tocut. The process employed directs a laser beam, of sufficient energy andduration, against the line 18. For the above described lines, a laser,such as is sold by the ESI company having a beam energy of 2microjoules, a diameter of between 6 and 7 microns and a pulse width ofabout 9 nanoseconds is directed against the line for about 9nanoseconds.

In FIG. 3, the beam, being applied, is indicated by the dotted circle30. The beam energy is absorbed by the line 18 causing the area of theline under the beam to be super heated and vaporized. When the areaunder beam vaporizes, the line is severed i.e., the fuse is blown.Because of the rapidity of the vaporization of the line 18 under thebeam a large section of the overlying passivation layer 22 is blown awayleaving a large, substantially circular crater 32 centered around theposition where the beam impinged on the line 18. It should be noted thatthe crater created by the removal of the overlying passivation layerextends over the adjacent lines 16 and 20 exposes them. When these linesare so exposed they become subject to corrosion which can result insubsequent failure of these lines and premature failure of the circuit.It has further been found that some of the beam energy is reflected ofthe positive sloped sides of the line 18 and this energy is directedtowards the adjacent lines 16 and 20 and causes melting or erosion of aportion of these lines 16 and 20 exerting additional pressure and stresson the adjacent lines 16 and 20. If the lines are sufficiently close,the amount of melting can be sufficient to cut through the lines. Evenif the melting of the lines is insufficient to sever the lines 16 and 20it can still be severe enough to cause a change in the resistivity ofthe line thus creating undesirable circuit changes. Finally, in somecases, extensive cracks have been found to radiate, through thepassivation layer, out from the crater causing one or more of theadjacent lines to be broken. This inadvertent breaking of a line, thatwas not selected to be broken, leads to significant production losses.

To avoid these problems the prior art could only increase the center tocenter spacing of the lines to an extent that such effect did not occur.This prior art solution does not permit optimum circuit layout.

The present invention as shown in FIGS. 5 to 8 avoids all the problemsencountered in the prior art while maintaining the smallest presentlyachievable, center to center, inter-line spacing.

FIG. 5 is created using the steps described above to create the deviceshown in FIG. 1 and like numerals refer to like features. However, thedevice shown in FIG. 5 is further treated following the planarization ofthe passivating layer 22 by again masking the surface of layer 22 withphotoresist, and patterning it so the layer 22 can be provided with aplurality of grooves 40 approximately 0.9 microns in width and ofsufficient depth to extend at least halfway down the thickness of themetal lines 16, 18, and 20. Reactants such as a halogen or halogen basedcompounds may be used, with materials such as Fluorine, or CarbonTetrafluoride (CF₄) or Carbon Trifluoride (CHF₃) being especiallypreferred for etching SiO₂. Photoresist is unaffected by these RIEetchants thus it not only protects the underlying passivation layer 22,except where the layer is exposed by patterning of the photoresist, butalso defines the width of the grooves 40. As a result of the anisotropicnature of this RIE process, the sidewalls of the grooves 40 are sharplydefined and are substantially perpendicular to the surface of the oxidepassivating layer 22.

The separation of the grooves 40 must be greater than the diameter ofthe laser beam. In the present example, the lines 16, 18, and 20 arepositioned 7.2 microns center to center. This means that, with a 6-7micron wide laser beam the grooves 40 can be placed midway between theline 18 and the surrounding lines 16 and 20. Once the grooves 40 aredefined they are filled with a non-frangible, high melting pointmaterial 41. In the present invention the material selected wastungsten. But other suitable materials which are not easily broken andwhich have melting points greater than the melting points of the fusebeing blown such as molybdenum can be used.

Tungsten was selected, in the present example, because tungsten iswidely used for filling the via holes and is used as the interconnectingmaterial between wiring layers in integrated circuits. Although in thepresent invention no additional layer is shown over the passivationlayer 22, additional metallization layers, as will be described inconjunction with FIGS. 9 and 10, could be so provided and the groovescould be made and back filled during the via hole opening and fillingsteps needed to create the interconnections between levels.

Again it will be assumed that to achieve the desired configuration it isnecessary that the central line 18 is to cut. Again a laser beam,indicated in FIG. 7 by circle 50, that is identical, in all respects, tothe one described above is directed against the line 18 such that thebeam energy is absorbed by the line 18 to vaporize the portion of line18 where the beam impinges as above described. Again because of therapidity of the vaporization of that portion of line 18 under the beam alarge section of the overlying passivation layer 22 is blown away.

Now however, the barriers 41 disposed in the grooves 40 confine theforces engendered by the line vaporization and prevents the formedcrater 34 from expanding sufficiently to reach the adjacent lines 16 and20. Thus, instead of leaving in the overlying passivation layer a large,substantially circular crater centered abound the point of impact of thebeam 30 a more rectangular crater, whose sides are defined by thebarriers 41, is created.

It should be noted, the barriers 41 extend at least half way down thethickness of the metal lines 16, 18, and 20. That is, the barriers mustextend at least to the midpoint of the thickness of the fuse. By sopositioning the barriers 41, not only is the cratering effect containedbut substantially all of the beam energy reflected from the positivelysloped sides of the line 18 is prevented from reaching the adjacentlines 16 and 20. Any energy that does reach the adjacent lines isinsufficient to melt or otherwise physically alter the adjacent lines.Also it should be noted that the barriers are formed of a material thathas a melting point substantially higher than the melting point of thelines 16, 18, and 20 thus any reflected energy is insufficient to meltthese barriers. Preferably the melting point of the barrier materialshould be at least 50% higher than the melting point of the fuses. Thebarriers 41 should also be resistant to cracking in order to prevent anycracks propagated in the passivation layer from reaching the adjacentlines 16 and 20.

Because the cratering of the overlying passivation layer is preventedfrom extending over the adjacent lines 16 and 20 they do not becomeexposed and are not subject to corrosion. By preventing the possibilityof such corrosion the quality and expected life of the product isenhanced. These barriers also prevent any cracks from extending over toone or more the adjacent lines further enhancing the quality of theproduct and cutting production losses.

By avoiding these problems encountered by the prior art, optimum circuitlayout, denied to the prior art, can be achieved.

The present invention as shown in FIGS. 5 to 8 thus avoids all theproblems encountered in the prior art while maintaining the smallestpresently achievable inter-line spacing.

FIGS. 9 and 10 show a semiconductor substrate provided with a stack ofwiring layers. Starting as before with a substrate 50 having activeregions (not shown) therein and a dielectric layer 52 disposed on itstop surface 51, a first passivated wiring level 53 is provided over thedielectric layer 52. Once this first wiring layer 53 is created, viaconnections are provided to it and an additional passivated wiring level54 having a fuse array is similarly created thereon. For clarity ofillustration, and because such multilayered wiring is well known to theprior art, only the fuse array formed of lines 56, 57, and 58 and theassociated barriers 59, are shown in these FIGS. 9 and 10. The otherwiring in each level and the interconnections therebetween are not shownin these FIGS. 9 and 10. Following the formation of the fuse containingwiring level 54 a capping passivated wiring level 55 is deposed thereon.

It should be noted that the barriers must be in the uppermost layer asshown in FIGS. 5 to 8 or extend to the surface of the capping layer 55,as shown in FIG. 9 or else the capping layer 55 should be removed downto the top of the barriers 59 as shown in FIG. 10.

This completes the description of the preferred embodiment of theinvention. Since changes may be made in the above process withoutdeparting from the scope of the invention described herein, it isintended that all the matter contained in the above description or shownin the accompanying drawings shall be interpreted in an illustrative andnot in a limiting sense. Thus other alternatives and modifications willnow become apparent to those skilled in the art without departing fromthe spirit and scope of the invention as set forth in the followingclaims.

What is claimed is:
 1. A method of protecting elements formed on thesurface of an substrate adjacent a fusible link comprising the stepsof:selecting a substrate:depositing an insulating layer on the surfaceof said substrate; depositing a metallic layer on said insulating layer;forming a plurality of elements, including a fuse, in said metalliclayer; coating said fuse and said elements with a passivating layer;treating said passivating layer to form grooves between said fuse andany adjacent element; and depositing a metal having a melting pointhigher than the melting point of the fuse in said grooves.
 2. A methodof protecting circuit elements in a wiring layer formed on the surfaceof an integrated circuit adjacent a fuse comprising the stepsof:selecting a semiconductor body:forming a plurality of active regionstherein; depositing an insulating layer on the surface of saidsemiconductor body having the active regions therein; depositing ametallic wiring layer on said insulating layer; forming a plurality ofcircuit elements, including a fuse, in said wiring layer; formingconnectors, through said insulating layer, between said wiring layer andsaid active regions; coating said fuse and said elements with apassivating layer; treating said passivating layer to form groovesbetween said fuse and any adjacent element; and depositing a metalhaving a melting point higher than the melting point of the fuse in saidgrooves.